In order to solve the problem of obstacle avoidance for unmanned surface vehicles (USV), based on the classic RRT algorithm and Velocity Obstacle principle, an improved RRT algorithm is proposed. For the situation of the extension direction of the parent node inside the collision cone in the EXTEND operation, ‘obstacle repellent vector’ and ’collision risk index’ are presented, making the extension direction of the search tree have the tendency to move away from obstacle. Meanwhile for the problem of the real time performance of the algorithm and path oscillation, ‘target attraction vector’ and waypoint corner constraint are introduced to accelerate the convergence of the algorithm and improve the quality of path point. Path planning experiment results show that the improved algorithm has better real-time character. Path tracking experiment results based on 3-DOF ship nonlinear dynamic model reveal that the collision-free paths generated by improved RRT algorithm are smoother and the navigation time is shorter, which are of great significance for practical engineering application.

This study addresses the oil trapping phenomenon in the operation of external meshing gear pumps by proposing a design of unload groove gear pumps with optimized tooth profiles, based on performance requirements and design specifications. The internal flow field of the gear pump is characterized using a standard turbulence model, and computational fluid dynamics (CFD) is employed to model and simulate unload groove gear pumps with different tooth profiles. Based on the analysis of the internal flow characteristics and pressure distribution, the optimized unload groove significantly alleviates the oil trapping issue. Among the tested tooth profiles, the high-tooth profile demonstrates the best performance, achieving optimal flow characteristics and volumetric efficiency with minimal increase in axial load when combined with the unload groove. This study highlights the critical role of tooth profile optimization in improving the performance of external meshing gear pumps and provides valuable references for gear pump design and analysis.

To improve the problem of oil trapping during the operation of external gear pumps, studies on the design of external gear pump teeth and unload groove and the analysis of the effect of their flow characteristics have been carried out. An external gear pump with a new type of unload groove was designed with reference to the general design specification. Based on the computational fluid dynamics (CFD) method, a numerical simulation model of the internal flow field of the gear pump was established, and the simulation analysis of the internal flow characteristics and pressure distribution of the gear pump was carried out to obtain the influence law of unload groove on the performance of the gear pump. The simulation results showed that the unload groove gear pump had a better flow rate, higher capacity efficiency, and less radial pressure than the Default gear pump under the same working conditions and design parameters. The study showed that the external gear pump with unload groove designed in this paper has significantly improved the problems caused by the oil trapping problem compared with the default gear pump.